Flight Instruments Flashcards
1
Q
What instruments operate from the pitot/static system?
A
The pitot static system operates the altimeter, vertical speed indicator, and airspeed indicator
2
Q
How does an altimeter work?
A
In an altimeter, aneroid wafers expand and contract as atmospheric pressure changes, and through a shaft and gear linkage, rotate pointers on the dial of the instrument.
3
Q
What are the limitations that a pressure altimeter is subject to?
A
Nonstandard pressure and temperature. Temperature variations expand or contract the atmosphere and raise or lower pressure levels that the altimeter senses.
- On a warm day - the pressure level is higher than on a standard day. Altimeter indicates lower than actual
- On a cold day - pressure level is lower than on standard. Indicates higher than actual
Changes in surface pressure also affect pressure levels at altitude.
- higher than standard pressure - the pressure level is higher than on a standard day. The altimeter indicates lower than actual altitude
- Lower than standard pressure - the pressure level is lower than standard. Indicates higher than actual
High to low or hot to cold look out below
4
Q
What is the maximum allowable error for an altimeter IFR flight
A
75 feet
5
Q
Define indicated altitude.
A
read on the face of altimeter
6
Q
Define pressure altitude.
A
altitude above the 29.92” Hg plane
7
Q
Define true altitude.
A
Height above sea level. Use the flight computer to determine.
8
Q
Define density altitude.
A
Pressure altitude corrected for nonstandard temperature
9
Q
Define absolute altitude.
A
Height above ground. Determined by subtracting the terrain elevation from true altitude.
10
Q
How does the airspeed indicator operate?
A
The airspeed indicator measures the difference between ram (dynamic) pressure from the pitot tube to a diaphragm and atmospheric (static) pressure from the static source into the case of the instrument. The diaphragm is mechanically linked to the needle.
11
Q
What are the limitations the airspeed indicator is subject to?
A
- Pitot blocked: Reads 0
- Pitot and drain blocked: Acts like an altimeter (higher=faster, lower=slower)
- Static blocked: Acts like a reverse altimeter (higher=slower, lower=faster)
- Static and pitot blocked: freezes
12
Q
What are the errors that the airspeed indicator is subject to?
A
- Position error - Static ports sense erroneous static pressure; slipstream flow disrupts. Varies with airspeed, altitude, configuration
- Density error - changes in altitude and temperature are not compensated for by instrument
- Compressibility error - caused by the packing of air into the pitot tube at high airspeeds, resulting in higher than normal indications. Usually above 180 KIAS
13
Q
Define Calibrated Airspeed (CAS).
A
The airspeed indicator reading corrected for position and instrument errors; equal to TAS at sea level in standard atmosphere. The color coding for various design speeds marked on the airspeed indicators may be IAS or CAS
14
Q
Define Equivalent Airspeed (EAS)
A
The airspeed reading corrected for position instrument error and for adiabatic compressible flow for the particular altitude; equal to CAS at sea level in standard atmosphere
15
Q
Define True Airspeed (TAS).
A
the speed of the airplane in relation to the air mass in which it is flying
16
Q
What are the different types of airspeeds?
A
Indicated - Instrument
Calibrated - POH
Equivalent
True - E6B
17
Q
Define the green arc on the airspeed indicator.
A
normal operating range
18
Q
How does the vertical speed indicator work?
A
Static pressure is connected directly to the diaphragm, which drives mechanical linkages to the needle on the face of the instrument. A calibrated leak at the back of the case of the instrument prevents the pressure outside the diaphragm from changing instantly. This pressure differential causes the diaphragm to expand/contract, indicating a change in vertical speed.
19
Q
What are the limitations of the VSI?
A
It is not accurate until the aircraft is stabilized. Sudden or abrupt changes in the aircraft attitude will cause erroneous instrument readings as airflow fluctuates over the static port. These changes are not reflected immediately by the VSI due to the calibrated leak
20
Q
What instruments are affected when the pitot tube ram air inlet and drain hole freeze?
A
Only the airspeed indicator will be affected. It acts like an altimeter - it reads lower than actual speed in level flight. Reads higher as aircraft climbs and lower as aircraft descents.
21
Q
What instruments are affected when the static port freezes?
A
Airspeed indicator - behaves like an altimeter, but in reverse (higher = slower, lower = faster)
Altimeter - indicates the altitude at which system blocked
VSI - will indicate level flight
22
Q
If the air temperature is +6 celcius at an airport elevation of 1,200 feet and standard temperature lapse rate, what will approximate freezing level be?
A
4,200 MSL; 6 divided by average temperature lapse rate of 2 results in a 3000 foot freezing level, add 1200
23
Q
What corrective action is needed if the pitot tube freezes? Static?
A
Pitot - turn on pitot heat
Static - use alternate air if available or break the face of a static instrument (either VSI or A/S indicator)
24
Q
What indications should you expect while using an alternate static source?
A
If it is vented inside the aircraft
- Altimeter - will indicate higher than actual
- Airspeed - will indicate greater than actual airspeed
- VSI - will indicate a climb while in level flight
This is because slipstream usually causes lower pressure inside the aircraft vs ambient pressure
JIC 2-25
25
Name several types of power sources commonly used to power the gyroscopic instruments in an aircraft.
* electrical
* pneumatic
* Venturi tube
* wet type vacuum pump
* dry air pump systems
Aircraft and instrument manufactures have designed redundancy into the flight instruments so that any single failure will not deprive the pilot of his ability to safely conclude the flight. Gyroscopic instruments are crucial for instrument flight; therefore they are powered by separate electrical or pneumatic sources. Typically, the heading indicator and attitude indicator will be vacuum driven and the turn coordinator electrically.
** CONSULT POH
26
How does the vacuum system work?
* The vacuum or pressure system spins the gyro by drawing a stream of air against the rotor vanes to spin the rotor at high speeds, essentially the same as a water wheel or turbine operates
* The amount of vacuum or pressure required for instrument operation various but is usually between 4.5-5.5 in Hg
* A typical source of vacuum for gyros installed in light aircraft is the vane type engine driven pump, mounted on the accessory case of the engine
27
How does the turn coordinator operate?
The turn part of the instrument uses gyroscopic precession to indicate direction and approximate rate of turn. A gyro reacts by trying to move in reaction to the force applied thus moving the miniature aircraft in proportion to the rate of turn. The inclinometer measures the relative strength of the force of gravity and the force of inertia causes by a turn.
28
What information does the turn coordinator provide?
Rate of turn, rate of roll, and direction of turn. The inclinometer indicates quality of turn (slip and skid)
29
What is the source of power for the turn coordinator?
Either by air or electricity, typically electrically powered
30
How does the heading indicator work?
The operation of the heading indicator works on the principle of rigidity in space. The rotor turns in a vertical plane, and fixed to the rotor is a compass card. Since the rotor remains fixed in space, the point on the card holds the same position in space relative to the vertical plane. As the instrument case and the airplane revolve around the vertical axis, the card provides clear and accurate heading information.
31
What are the limitations of the heading indicator?
They vary with the particular design and make of instrument: on some, limits are approximately 55 degrees pitch and 55 bank. When either of these attitude limits are exceeded, the instrument tumbles and no longer gives correct indication until reset. Many modern instruments used are designed in such a manner that they will not tumble.
32
What type of errors is the heading indicator subject to?
* **Apparent drift** - The earth rotates 15 degrees every hour, every 15 min will be off about 3.5 degrees.
* **Bearing Friction** - Causes creep or drift from set position
Both are resolved by syncing the HI to the compass every 15 min
33
What are the limitations of the heading indicator?
They vary with the particular design and make of instrument: on some, limits are approximately 55 degrees pitch and 55 bank. When either of these attitude limits are exceeded, the instrument tumbles and no longer gives correct indication until reset. Many modern instruments used are designed in such a manner that they will not tumble.
34
How does the attitude indicator work?
A gyro mounted on a horizontal plane. It operates upon rigidity in space.
35
What are the limitations of an attitude indicator?
Older attitude indicators were limited to about 60° pitch and 100° of roll. This was because when exceeding these limits, the gyro housing contacts the gimbals, applying a precessing force that causes the gyro to tumble
36
Is the attitude indicator subject to errors?
It is free from most errors, but there may be a slight nose up indication during a rapid acceleration and a nose down indication during a rapid deceleration.
37
How does the magnetic compass operate?
Magnets mounted on the compass card align themselves parallel to the Earth's lines of magnetic force
38
What limitations does the magnetic compass have?
The jewel and pivot type mounting gives the float freedom to rotate and tilt up to approximately 18 degrees angle of bank. At steeper bank angles, the compass indications are erratic and unpredictable.
39
Define oscillation.
A magnetic compass error, turbulence or rough control technique causes erratic movement of the compass card
40
Define Deviation.
Magnetic compass error, due to electrical and magnetic disturbances in the aircraft
41
Define variation.
Magnetic compass error, angular differences between true and magnetic north. Reference isogonic lines of variation to resolve
42
Define Magnetic Dip.
The Earth's magnetic field only runs parallel to its surface at the equator. As you move closer to the poles, the angle created by the vertical pull of the Earth's magnetic field in relation to the Earth's surface increases gradually, known as dip. This increases in a downward direction as you move towards the North Pole and upward as you move towards the South Pole.
Resolved by lowering the CG below the pivot point to negate the vertical component of magnetic force.
43
Which instruments utilize pitot static sources?
* Air Speed Indicator
* Vertical Speed Indicator
* Altimeter
| PHAK 8-2
44
Which instrument is the only instrument to utilize the pitot tube?
Air Speed Indicator (ASI)
| PHAK 8-2
45
What instrument indications are observed when an alternate static source pressure is used?
1. Altimeter indicates a slightly higher altitude than actual
2. ASI indicates an airspeed greater than the actual airspeed
3. VSI shows a momentary climb and then stabilizes if altitude remains constant
| PHAK 8-3
46
If an aircraft is not equipped with an alternate static pressure source, what can the pilot do to introduce static pressure to the system?
break the glass face of the VSI
| PHAK 8-3
## Footnote
We break the VSI because this is the lease important static source instrument for flight, and will likely render the instrument inop
47
How does an altimeter operate?
A stack of sealed aneroid wafers set to an internal pressure of 29.92 "Hg are free to expand and contract with changes to static (ambient) pressure. Higher static pressure (lower altitude) squeezes the wafers and causes them to collapse. Lower static pressure (higher altitude) allows the wafers to expand. A mechanical linkage connects the wafer movement to the needles on the indicator face.
| PHAK 8-3
48
How does a change in pressure effect the altimeter?
* If the aircraft is flown from a high pressure area to a low pressure area, a constant altitude would be displayed but the actual height AGL would be lower than the indicated altitude. "FROM HIGH TO LOW, LOOK OUT BELOW"
* If flown from low pressure to high pressure, the true altitude of the aircraft is higher than the indicated altitude
| PHAK 8-4
49
How does nonstandard temperature effect the altimeter?
* When operating in temps that are colder than standard, the true altitude is lower than indicated. Differences due to colder temps are of primary concerns to the pilot. "FROM HOT TO COLD, LOOK OUT BELOW"
| PHAK 8-4
50
How is altimeter setting defined?
Station pressure reduced to sea level
| PHAK 8-5
51
How can a pilot determine the amount of altimeter error from original setting to a new reported setting?
Subtract the new setting from the original setting. Since 1 inch of pressure is approximately 1000 feet, multiply by 1000. Then subtract that number from the indicated altitude.
| PHAK 8-6
52
Define Indicated Altitude
read directly from the altimeter (uncorrected) when it is set to the current altimeter setting
| PHAK 8-6
53
Define True Altitude
the vertical distance of the aircraft above sea level--the actual altitude. Often expressed as ft MSL. Airport, terrain, and obstacle elevations on aeronautical chares are true altitudes
| PHAK 8-6
54
Define Pressure Altitude
the altitude indicated when the altimeter setting is adjusted to 29.92 "Hg. This is the altitude above the standard datum plane, which is a a theoretical plane where air pressure (corrected to 15 degrees C) equals 29.92 "Hg. Pressure altitude is used to compute density altitude, true altitude, true airspeed, and other performance data.
| PHAK 8-7
55
Define Density Altitude
Pressure altitude corrected for variations from standard temperature. When conditions are standard, pressure altitude and density altitude are the same. If temperature is above standard, the DA is higher than pressure altitude. If temp is below standard, the DA is lower than pressure altitude. This altitude is directly related to aircraft performance.
| PHAK 8-7
56
Define Absolute Altitude
The vertical distance between the aircraft and terrain, ft AGL
| PHAK 8-7
57
What is the allowable amount of error for the altimeter before it must be recalibrated?
75 feet from surveyed field elevation
| PHAK 8-7
58
Describe how the VSI operates
The VSI contains a diaphragm which is linked to the indicator inside an airtight case. The inside of the diaphragm is connected directly to the static link of the pitot-static system. The area outside the diaphragm is connected to the static line but through a restricted orifice (calibrated leak). Because the diaphragm receives unrestricted air and the case is restricted, changes in static pressure create a differential for a short time, indicating a climb or descent.
| PHAK 8-7
59
What types of information does the VSI indicate?
1. Trend information - shows an immediate indication of an increase or decrease in rate of climb or descent
2. rate information - shows a stabilized rate of change in altitude
| PHAK 8-8
60
Describe how the ASI operates
The ASI contains a diaphragm which is linked to the indicating sytem. The ASI case is connected to the static system, while the pitot pressure is introduced into the diaphragm. The dynamic pressure from the pitot tube expands one side of the diaphragm as airspeed (and pressure) increases, and contracts when airspeed decreases.
| PHAK 8-8
61
Define Indicated Airspeed
The direct instrument reading obtained from the ASI, uncorrected for variations in atmospheric density, installation error, or instrument error. Used to determine aircraft performance. Takeoff, landing, and stall speeds listed in the AFM/POH are IAS and do not normally vary with altitude or temp.
| PHAK 8-8
62
Define Calibrated Airspeed
IAS corrected for installation error and instrument error. Generally greatest at low airspeeds. Refer to airspeed calibration chart to correct for possible airspeed errors.
| PHAK 8-9
63
Define True Airspeed
CAS corrected for altitude and nonstandard temp. TAS increases as altitude increases because air becomes less dense, therefore causing differential pressure to decrease between pitot and static pressures. This can be computed with a flight computer, or in a pinch, by adding 2% to CAS for each 1000' of altitude. TAS is the speed used for flight planning and when filing a flight plan.
| PHAK 8-9
64
Define Groundspeed
The actual speed of the airplane over the ground. It's TAS adjusted for wind.
| PHAK 8-9
65
Define V*be*
Best endurance, where the helicopter can maintain altitude the longest
66
Define V*ne*
Never exceed speed, even in a dive
| PHAK 8-9
67
Define V*nea*
Never exceed speed for autorotations
68
Define V*neao*
Never exceed speed with augmentation (SAS, SCAS or other) off
69
Define V*bg*
Speed of best glide range, at which the helicopter can fly the maximum distance without power (autorotate)
70
Define V*br*
Speed of best range, at which the helicopter can fly the longest distance given an amount of fuel
71
Define V*c*
speed of cruise, convenient overall speed for fuel efficiency, transit time, maintenance and handling qualities
72
Define V*g*
Speed of glide, at which the helicopter has the smallest descent rate (best endurance) without power (in autorotation)
73
Define V*h*
Speed of max continuous power (MCP), at which the helicopter will consume the max power it can sustain level flight
74
Define V*aft*
Never exceed speed in aft flight
75
Define V*lat*
Never exceed speed in lateral flight
76
Define V*taxi*
Never exceed speed in taxi operations
77
Define V*x*
Speed at which the steepest climb angle is obtained (typically 0, giving a 90 degree vertical climb)
78
Define V*y*
Speed at which the helicopter can climb fastest
79
Define V*tocs*
recommended speed for takeoff and climb out
80
Define the difference between endurance and range
Endurance is purely fuel-burn focused. Range takes into account speed.
Eg.
We have a helicopter that burns 200 pounds of fuel per hour (PPH) at 50 KIAS, and 300 PPH at 100 KIAS. Of course, the helicopter can fly for a longer time at 50 KIAS because less fuel is burned per second. However, it can fly further at 100 KIAS. The math follows.
While any amount would work, let's just assume the helicopter has 300 pounds of fuel. It can fly at 50 KIAS for 300/200 or 1.5 hours, but it can only fly at 100 KIAS for 300/300 or 1.0 hours (i.e. it has better endurance at 50 KIAS). However, notice that it can only fly 50 KIAS times 1.5 hour or 75 nautical miles in the 1.5 hours at 50 KIAS, while it can fly 100 KIAS times 1 hour or 100 nautical miles at 100 KIAS (i.e. it has a better range at 100 KIAS)!
81
Explain the required instrument check for the ASI
Prior to takeoff, ASI should read zero (unless there is a strong headwind). When beginning takeoff, ensure airspeed is increasing at an appropriate rate.
| PHAK 8-10
82
Describe what would be observed if the pitot tube becomes blocked and the pitot drain hole and static hole remain open.
Ram air is no longer able to enter the system. Air already in the system vents via the drain hole, and remaining pressure drops to ambient pressure. The ASI reads 0 because it senses no difference between ram and static air pressure.
| PHAK 8-10
83
Describe what would be observed if the pitot tube opening and drain hole become blocked simultaneously.
Pressure in the pitot tube would become trapped. No change would be observed on the ASI despite airspeed changes. If the static port is unblocked and the aircraft changes altitude, the ASI would indicate a change, basically behaving as an altimeter.
84
Describe what would be observed if the static system becomes blocked but the pitot tube remains clear
**ASI** will continue to operate, but will be inaccurate. The airspeed indicates lower than actual airspeed when the aircraft is operated above the altitude at which the static ports became blocked because the trapped static pressure is higher than that of the ambient pressure at that altitude. The opposite is true when operated at a lower altitude.
**Altimeter** will freeze at the altitude where the block occured.
**VSI** will show a continuous zero indication.
85
What are the primary gyroscopic instruments?
* Turn coordinator
* heading indicator
* attitude indicator
| PHAK 8-15
86
What are the two fundamental properties of gyroscopic instruments?
* Rigidity in Space - a gyroscope remains in a fixed position in the plane in which it is spinning
* Precession - the tilting or turning of a gyro in response to a deflective force. The reaction to this force occurs 90 degrees later in the direction of rotations
87
Describe the difference between a turn coordinator and a turn and slip indicator
Both of these instruments provide rate of turn information and slip/skid indications. The turn coordinator also provides banking indications and roll rate
88
When using a GPS for IFR navigation, are you required to have an alternate means of navigation appropriate for the route of flight?
* Only if it is non-WAAS
* Active monitoring of alternative nav equipment is not required if the receiver uses RAIM
89
Does an aircraft have to remain stationary during AHRS system initialization?
Some AHRSs must be initialized on the ground prior to departure. The initialization procedure allows the system to establish a reference attitude used as a benchmark for all future attitude changes. Others are capable of initialization while taxiing or in-flight.
| Advanced Avionics Handbook
90
What display information will be lost when an ADC failure occurs?
* Airspeed
* Altitude
* VSI
Red Xs
91
What display information will be lost when an AHRS failure occurs?
attitude indicator (red X)
92
How will loss of a magnetometer affect the AHRS operation?
Heading information will be lost.
